93 300se automatic belt tensioner

I replaced my drive belt on my 300se,taking the old belt out was easy,by pulling on the belt tension and slip it out of the pully.But when I try to put in the new belt the belt was too loss. I cannot get any tension from the auto tensioner and the adjuster cannot help either.Iwonder is my auto tensioner need replacement.Need helpTHanks I use mercedes original belt,I try putting back the old belt still, too loose.I used the edit button because I do not know how to sent another message .Sorry. thanks for your fast respond.need more help

[vinamg]

Double check that your new belt is the same length. Actually, the new one should be slightly shorter.

Vin

[engatwork]

I would get the manual out and make sure you are installing it correctly also make sure you have not loosened something up that is preventing the tensioner from tightening back up.